System for generating rhythm tones



y 21, 1964 SHIGEAKI MABUCHI 3,141,919

SYSTEM FOR GENERATING RHYTHM TONES Filed Sept. 26, 1960 2 Sheets-Sheet 1Output voltage time y 21, 1964 SHIGEAKI MABUCHI 3,141,919

SYSTEM FOR GENERATING RHYTHM TONES 2 Sheets-Sheet 2 Filed Sept. 26, 1960Figw 8W Fi gwglp United States Patent YSTEM FOR GlENERATlNG RHYTHMTtlNES Shigealri Mahuchi, Hamamatsu-shi, Japan, assignor to JNihonGaltlri Seize Kabushiki Kaisha, Hamamatsu-shi,

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Filed Sept. 26, 1969, Ser. No. 58,226 Claims priority, application JapanOct. 23, 1959 1 Claim. (Ci. 84--1.26)

This invention relates to electrical musical instruments, and moreparticularly it relates to a new system for creating rhythm tones in apurely electronic manner.

One conceivable method of electrically creating sounds resembling thesounds of such rhythm instruments as cymbals, triangles, and drums isthe conventional method of using a thyratron or other noise generatingdevices as a noise generating source and utilizing the noise amplifiedtherefrom. The noise obtained from such a noise source is passed througha suitable filter circuit to shape a wave form having the requiredfrequency spectrum.

A system relying on such a method, however, entails the followingdisadvantages. In the first place, it is ditficult to obtain the desiredfrequency spectrum by means of a simple filter circuit except in specialcases. Accordingly, the tone colors with unique qualities, obtainedtherefrom become extremely restricted in number. Conversely, if tonecolors with ample unique qualities are to be created in great number,the filter circuit will tend to become complex. In the second place, thesounds generated from rhythm instruments are so-called percussivesounds. Such sounds have a wave form wherein the sound wave risesabruptly at the instant of percussion, and its attenuation isexponential. In many cases, the numher of noise like components is largeduring the rise period while at its peak. During the attenuation, thevibration at the natural frequency, which is determined by such factorsas the configuration and material of the musical instruments, becomesintense, and almost all of the noise like components, disappear. Forthis reason, if a wave obtainable from a noise source is processed withthe aim of producing a tone approximating that of a musical instrument,a sound sensation of discord will be produced during attenuation.

The details of the invention will be more clearly apparent by referenceto the following detailed description of the invention when taken inconnection with the accompanying drawings, in which the same orequivalent parts are designated by the same reference numeral orletters, and in which:

FIG. 1 is a schematic, block diagram showing one example of theinvention.

FIGS. 2, 4, 5, and 7 are graphical representations of the output voltagewave forms of the various circuit elements of the embodiment of FIG. 1.

FIGS. 3, 6, 8, 9, and 10 are electrical circuit diagrams showing circuitelements for embodying the system of the invention.

In FIGURE 1 is shown a driving circuit 1; a resonance circuit 2 whichproduces vibrations when it is driven by the driving circut 1; anamplifier 3 which amplifies the signal voltage obtained through saidcircuits; a loudspeaker 4 for converting the amplified electric outputinto sound output; and a contact mechanism 5 for keying the drivingcircuit 1. The contact mechanism 5 is adapted to be normally controlledby the keys of a keyboard.

FIG. 2 shows a graph ot'output voltage versus time, representing thevoltage wave form obtained from the driving circuit 1 of FIG. 1. Theparticular condition shown is that for the time period when the contactmechanism 5 has been closed. As shown in FIG. 2, this wave form consistsof an abrupt rise in output voltage at the ice time of closing thecontact and a decrease in output voltage thereafter. This wave form isherein called the driving wave. When the driving wave is impressed oncircuit 2, there is produced oscillation at the frequency determined bythe parameters of the circuit components. This oscillation is damped bythe envelope effect of the driving wave. The manner in which thisattenuation occurs is in fluenced principally by the quality factor Q ofthe resonance circuit and not to a great degree by the character of theattenuation of the driving voltage.

The voltage wave form obtained in the above manner is amplified to thenecessary magnitude by the amplifier 3 and is converted into soundoutput by the loudspeaker 4. By presetting the resonance frequency ofthe resonance circuit 2 to the frequency which best expresses th musicalsensation created by the musical instrument to be represented, theobject of the invention is attained.

For the practical realization of the driving circuit 1 in an extremelysimple manner, a charging and discharging circuit composed essentiallyof only capacitors and resistors is sufiicient as is indicated by oneexample shown in FIG. 3. The driving circuit 1 is connected to a contactmechanism 5 and comprises: a capacitor for charging and discharging 6; aresistor for charging 7; a resistor for discharging 8; a couplingcapacitor 9; a direct-current power source 11 supplying a potential of Vvolts; a junction point A connecting the capacitor 6, resistors 7 andi5, and capacitor 9; an output terminal B; and a ground terminal E, theelements being wire as indicated in FIG. 3. The contact mechanism 5contains a switch device 10, which is normally open. When said switchdevice 10 is closed, the electric charge which has been charged in thecapacitor 6 is discharged through the resistor 8. Since the resistanceof the resistor 8 is substantially lower than the resistance of theresistor 7, the voltage at the point A suddenly approaches the groundvoltage. If the switch device 10 is then opened, the recharging of thecapacitor 6 will begin through the resistor 7, and the voltage at thepoint A will assume a value close to the value resulting from thedivision of the power source voltage V volts by the resistors 7 and 8.The voltage wave form at the point A will be as indicated in FIG. 4,wherein i is the time at which the switch device 10 is closed, and t isthe time at which it is opened. This voltage is connected through thecapacitor 9 to an outside circuit and, at the same time, it isditferentiated by the resistance connected between the terminals B and Eand the said capacitor 9. As a result, the voltage wave form whichappears at the output terminal B is as indicated in FIG. 5.

An embodiment of a driving circuit wherein a transistor is used is shownschematically in FIG. 6. The said circuit is connected to a contactmechanism 5 containing a switch device 26 and comprises, in part: acapacitor 16 for charging and discharging 16; a resistor 17 forcharging; a resistor 18 for discharging; a coupling capacitor 19; adirect-current power source 21 (of V volts); and an output terminal B,said elements accomplishing the same functions as their equivalentelements shown in FIG. 3. In addition, the driving circuit 1 shown inFIG. 6 comprises a transistor 12 which has three electrodes, namely, anemitter electrode 13, a base electrode 14, and a collector electrode 15;resistors 22, 23, and 24; and an input terminal C. The above-statedelements are connected as schematically indicated in FIG. 6. Thetransistor 12 has the functions of correcting the charging anddischarging characteristics of the capacitor 16 and, simultaneously,transmitting the said charged or discharged voltage to the collectorelectrode 15 through the capacitor 19, which is coupled to the collectorelectrode 15. The resistors 22 and 23 are for the purpose of impartingsuitable bias voltage to the base electrode 14 of the transistor 12;and, by varying their resistance values, it is possible to vary thepoint at which the transistor 12 is changed from a conductive state to acut-off state. The resistor 24 is the load resistance of the transistor1.2 and is also one of the factors which determine the configuration ofthe attenuation curve of the voltage wave form illustrated in FIG. 4.The input terminal C is used when input from the outside is necessary.

Transistor 12; is normally in the cut-ofi state. When the switch device20 is closed, as the voltage of the emitter electrode 13 almost reachesthe ground voltage, the transistor becomes conductive. At this time, thevoltage of the collector electrode 15 suddenly changes from V volts tothe ground voltage. If the switch device is opened, the charging of thecapacitor 16 through the transistor 12 and through the load resistors 24and 17 begins; the voltage of the emitter electrode 13 graduallyapproaches V volts; and the transistor 12 is changed little by littleinto the cut-off state. The wave form of the changing voltage of thecollector during this operation assumes the same configuration as thatshown in FIG. 4, and a wave form as indicated in FIG. 5 is observable atthe output terminal B.

If an input, for example, a white noise voltage, is introduced throughthe input terminal C, the resulting wave form appearing at the outputterminal B will be a superposition of this input wave form on the waveform shown in FIG. 4. The said resultant wave form is indicated in FIG.7. In this case, the tone color obtainable will be of a diiferent kind.

One example of a simple embodiment of the resonance circuit 2 of FIG. 1is shown in FIG. 8, wherein the said circuit comprises couplingresistors 25 and 26; a capacitor 27; and a coil 28. The capacitor 27 andthe coil 28 determine the resonance frequency. Upon arrival of an inputfrom the driving circuit 1 of FIG. 1, a vibration at the said resonancefrequency occurs; then as the input signal fades out, this vibration isattenuated exponentially. However, the attenuation time differsdepending on the magnitude of the quality factor Q of the resonancecircuit. That is, resonance circuits with larger Q have longerattenuation times.

The increase of Q of the resonance circuit 2 to the extent oflengthening the vibration attenuating time to several hundredmilliseconds by means of a circuit as illustrated in FIG. 8 is normallynot simple, because the demand upon the capacitor 27 and the coil 28becomes severe. For cases wherein such long attenuation times are notrequired, satisfactory results are obtainable by means of the circuit inthe state shown, but when it is desired particularly to lengthen thevibration attenuating time, a circuit as represented by the embodimentshown in FIG. 9 can be used.

This embodiment has the arrangement of a kind of amplifier andcomprises: resistors for bias 29 and 30; a transistor 31; a loadresistor 32; an emitter resistor 33 for the said transistor; and aby-pass capacitor 34. The negative feedback circuit is composed of adirect-current blocking capacitor 35; a frequency eliminating circuit36, which imparts a sufliciently large attenuation with respect to onlya certain frequency; and a coupling resistor 37. In actual practice, asuitable circuit such as, for example, a parallel T circuit or a bridgedT circuit, may be used for the frequency eliminating circuit. Thecircuit of FIG. 9 has, furthermore, a direct-current power source 38(voltage V volts), an output terminal B, and an input terminal C.Although this circuit has the form of a selective amplifier, the circuitconstant is so predetermined that, when an input arrives, oscillation atthe frequency determined by the frequency eliminating circuit 36 occurs.

One method for causing this to occur is to provide a parallel T-circuitshown in FIGURE 10 having resistors 39, 40, 41 and capacitors 42, 43,44. If the resistance value of the resistor 41 is sufficiently small incomparison with the values of resistors 39 and 40, the circuit can beplaced in the desired condition. Also, the value of this resistance 41causes the equivalent Q of the entire circuit 4 of FIG. 9 to vary.Actually, by varying resistance 41, it is possible to cause the dampingtime of the oscillation to vary.

In comparison with the circuit of FIG. 8, the circuit of FIG. 9 has anoutput voltage which, at times, is of a magnitude such that it requiresalmost no amplification. In such cases, it has a functional capacitywhich includes that of the resonance circuit 2 of FIG. 1 and a part, orall, of that of the amplifier 3.

The object of creating rhythm tones may be achieved by connecting theabove-described circuits as indicated in FIG. 1, applying the necessaryamount of amplification, and causing the loudspeaker to produce thetones.

The tone colors thus obtained as a result may be thought of as being dueto the substitution of the mechanical constructions of actual drums andother percussive musical instruments by equivalent, electrical circuits.By this system, percussive tone effects can be amply expressed.Moreover, the elements of the circuits are extremely simple, and not asingle factor causing instability in operation nor a single point ofdifficulty in design is entailed. Especially, if the embodiments of FIG.3 and FIG. 8 are combined, not a single active element is containedtherein; the number of parts is small; and, moreover, the output voltageobtained is not one which requires much contribution from the amplifierto be connected thereafter. Accordingly, the system can be constructedat extremely low cost.

As was mentioned initially, the tone colors generated by rhythm musicalinstruments contain many noise factors during the rise period, and thevibratory tones due to natural frequencies become strong during theattenuation period. If this effect is to be realized, the followingmeasure, by way of example, may be taken. The circuits of FIG. 6 andFIG. 9 are combined; a white noise voltage is introduced through theinput terminal C of the circuit of FIG. 6; the time constant of thecircuit consisting of the capacitor 16 and the resistor 17 is diminishedto hasten the attenuation of the output voltage of the white noise; andthe resistor 41 of the circuit of FIG. 10 is so adjused and set that, inthe circuit of FIG. 9, the attenuation time can be long. If the abovedescribed measure is taken, a large amount of white noises will becontained during rising of the sound output and during production ofpeak output, and only the sound determined by the frequency of thecircuit of FIG. 9 will remain during the attenuation process.

In comparison with the case wherein, rhythm tones are created by meansof only noises, the use of the present system can produce tone colorswhich are more agreeable to the ear.

While only one resonance frequency was considered in the above describedembodiment, it is possible to in crease the number of resonance circuitssuch as the circuit 2 shown in FIG. 1; if necessary, thereby generatingtone colors with further special qualities. For the realization of sucha measure, it is possible, for example, to provide circuits having 11resonance frequencies by inserting in parallel n circuits each of whichis as shown in FIG. 8.

While particular embodiments of the present invention have beendescribed, it will, of course, be understood that the invention is notintended to be limited thereto, since many modifications can be made inthe above described details without departing from the nature and spiritof the invention, and it is contemplated by the appended claim to coverall such modifications as fall within the true spirit and scope of theinvention.

What I claim is:

In an electrical musical instrument, an arrangement for generatingpercussive sounds in a loudspeaker having a wave form wherein the soundrises abruptly at the instant of percussion and is exponentiallyattenuated, the vibrations at the natural frequency being intensifiedduring attenuation, the noise-like components of the sound 5 6 almostdisappearing, said arrangement comprising in comsource; a secondtransistor including an emitter bination; joined to said fifth lead lineacross an eighth bias rea first stage driving circuit and switchincluding a DC. sistor, a collector joined to said sixth lead lineacross power source and first and second lead lines therea ninth loadresistor; a by-pass capacitor in parallel from; a PNP transistorincluding an emitter joined 5 with said eighth bias resistor; a D.-C.blocking capacto said first lead line at a first junction point, a itorin series with frequency elimination means concollector joined to saidsecond lead line at a second nected between said collector and saidfifth lead junction point, a base with a base input line; a chargline; abase to said second transistor connected in ing and dischargingcapacitor in series between said series to said sixth and seventhcoupling resistors first junction point and said emitter; a third junc-10 of said second stage, tenth and eleventh bias resistors tion pointbetween said capacitor and said emitter, between said base and saidfifth and sixth lead lines; a third lead line from said third junctionpoint to a twelfth bias resistor between said base and said said firstlead line, a first resistor for charging and frequency eliminationmeans, and, an output line a switch in series in said third lead line; asecond to the loudspeaker connected to the junction of said resistoracting as a collector load between said sec- 5 collector and said D.-C.blocking capacitor. 0nd junction point and said collector; a thirdresistor acting as a discharge resistor between said second ReferencesCited in the file Of this Damnt and third junction points, the value ofsaid first re- UNITED STATES PATENTS sistor for charging beingsubstantially higher than said third resistor; fourth and fifthresistors acting 20 g "a f 3 as bias resistors between said first andsecond lines 2139O23 5 1938 respectively to said base input line; afourth junc- 2342338 g 1944 tion point between said second resistor andsaid 2482548 g f 1949 collector a four lead line from said fourthjunction O 1949 point acting as the output lead and a coupling capac- 52584386 Z? ge 1952 istor in said output lead; 2694954 K i e 1954 asecond stage resonance circuit including a coupling 2927282 E 1960 lineto said coupling capacitor sixth and seventh 2964654 1960 couplingresistors in series, connected to said coupling 3050642 R Ia am 1962line, and a capacitor and coil in parallel, between 30 ogers et a saidsixth and seventh resistors and, a third stage OTHER REFERENCESamplifying circuit including a second D.-C. source, VEB (Germanapplication) 1023957 Feb 6, 1958 fifth and sixth lead lines from saidsecond D.-C.

